Objective lenses for pixel-based optical recording consist of three or more elements per one set of a lens-set pair. Thus the lens system is heavy and costly. A low cost and lightweight objective lens system is highly desired because it enables employing servoing technologies for addressing data, which substantially reduces cost of optical data storage setup.
In general, the objective lenses are not compatible with the bit-based recording scheme such as CD, DVD and Blu-ray. Backward compatibility with such existing systems is also highly desired.
For commercial use of optical data storages, the recording medium must be interchangeable among many recording and retrieve configurations to render the data storage system usable for archive and distribution purposes. The lens systems currently found in the art do not effectively address interchangeability.
For page-based systems, optical design criteria relating to the required number of elements and allowable aberrations are not clear. Therefore minimum lens configurations of such compatible designs have not been identified.
Both page-based and bit-based recording requires high NA objective lenses. Usually, such a high NA lens for page-based system requires three or more spherical lens elements, which are not compatible with bit based recordings.
Designs using aspheric elements having NA of 0.74 are reported, however the working distance is very small (<0.1 mm) which prevents the lens from using thick recording medium required for high-density page-based recordings. To date media interchangeability has not been considered. Specifically, these systems are not compatible with bit-based recordings because aberration correction requirements are not completely satisfied. The small working distance prevents the design from being used with thick recording material for high-density recording applications.
Designs having a moderate NA of 0.5 using one, two and three elements have been reported, however media interchangeability is not a consideration. Specifically, addition to moderate NA, compatibility with bit-based recordings is not taken into account.
The objective lens for page-based optical data recording and retrieval generally consists of many lens elements (usually three or more) to accommodate high NA (equivalently a large field of view), thus the objective lens is costly and heavy.
What is needed is a low-cost and light weight lens design of a high NA objective lens with a reduced number of elements for optical data storage and retrieval for page-based systems having a capacity for interchangeable medium, for example that are also usable for bit-based optical recording and retrieval like CD, DVD and Blu-ray systems, where aberration correction is considered. What is also needed is an medium-interchangeable lens system that allows for a sufficient working distance to accommodate thick recording medium required for high-density recording to avoid crashing the objective lens to the media.